The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An aircraft is propelled by one or more propulsion assemblies comprising a turbojet engine housed in a tubular nacelle. Each propulsion assembly is attached to the aircraft by a pylon generally located under a wing or the fuselage.
A nacelle generally has a substantially tubular structure comprising an upstream section defining an air inlet, a middle section intended to surround a fan of the turbojet engine, a downstream section capable of accommodating thrust reversal means and intended to surround the combustion chamber of the turbojet engine, and is generally ended by an ejection nozzle whose outlet is located downstream of the turbojet engine.
In the present application, the upstream and the downstream are defined with respect to the air flow direction in the operating propulsion assembly in direct jet mode, the air inlet being located upstream with respect to the ejection nozzle located downstream of the nacelle.
The maintenance operations of the turbojet engine require an easy access to the turbojet engine. To this end, the nacelle generally comprises two openings located at the lateral wall of the middle section of the nacelle, on either side of the pylon connecting the turbojet engine to the aircraft.
These two openings are each capable of being closed thanks to two half-cowls pivotally mounted with respect to an axis substantially parallel to a longitudinal axis of the nacelle.
These half-cowls are displaced between a closed position according to which they close the openings of the nacelle, and an open position according to which they open the openings of the nacelle so as to allow an access to the turbojet engine for maintenance operations, the holding of these half-cowls in the open position being performed by means of support feet.
A drawback of this type of cowl is that the access to the turbojet engine is limited by the presence of support feet which hold the half-cowls in the open position. Furthermore, an unexpected closure of these cowls can happen at any time during a maintenance operation, which represents a significant hazard to the operators.
In order to overcome these drawbacks, a solution of the prior art, such as that described in the document FR 2 930 763, consists in expecting a nacelle whose upstream and middle sections form a unitary assembly, which may be displaced along rails mounted on the turbojet engine between a closed downstream position ensuring, with a downstream structure of the nacelle, the aerodynamic continuity of the nacelle, and an open upstream position allowing the access to the turbojet engine in order to perform maintenance operations.
The holding of the upstream structure of the nacelle in the closed position is performed at the pylon attaching the propulsion assembly to the aircraft, thanks to a plurality of hooks cooperating with corresponding elements positioned at the pylon.
The displacement of the upstream structure of the nacelle from its closed downstream position to its open upstream position is performed in two stages. Firstly, an operator unlocks the hooks, then opens several handles configured, when they are in the open position, to allow a slight rotation of the cowl in order to disengage the hooks from the elements of the pylon with which they cooperate.
Once the rotation of the cowl performed, the displacement towards the upstream of the upstream structure can occur.
This type of structure advantageously allows an operator to access more easily and safely the turbojet engine.
However, a first drawback is that the opening kinematic is relatively long and complex.
A second drawback is that this type of structure is fragile due to significant aerodynamic forces generated in flight at the area near the air inlet lip of the nacelle, area not connected to the rest of the propulsion assembly.
A solution to the problem of the fragility of the structure might be to provide longitudinal spars disposed over all the length of the upstream structure of the nacelle.
This solution is satisfactory from a structural point of view, in that the presence of rails allows starting again the aerodynamic forces generated at the air inlet lip of the nacelle. However, such spars significantly increase the mass of the nacelle and their presence is therefore not acceptable.